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Invasive plant expert advises on our Gunnera problem

In June Robin Payne, an invasive species expert from Scottish Natural Heritage visited Harris to look at, and give advise on how to tackle our Gunnera problem.  Gunnera, also known as Giant Rhubarb was introduced to Harris around 20 years ago and is now spreading out of control, blocking ditches and covering crofts. It is also a large problem in Western Ireland where it is now illegal to sell, cultivate and transport the plant.  Scottish Natural Heritage were keen to look at our trial efforts to control the plant. Harris is the only area in Scotland where the spread of Gunnera has been raised as a problem to date. However, it is known to have become established in the wild in several places along the west coast where its spread is likely to cause problems in the future.

Robin Payne and Roddy MacMinn from SNH looking visiting Urgha

SNH stressed the importance of controlling Gunnera now before it spreads any further . Robin Payne was positive about the possibility of eradicating it from Harris, providing a large amount of effort is put into controlling the plant over the next few years. 

How to control Gunnera

In 2010 the North Harris Trust trialled some control methods which included removing seed heads, digging out plants and spaying plants with herbicide. The Trust will be extending its efforts in the areas worst affected and would also like to encourage others to control it where it is appearing in their gardens and crofts.

Removing seed heads:  The large seed heads can release thousands of seeds that are spread by birds, wind, water and traffic. By removing seed heads it is possible to reduce future spread. If seed heads are cut off before mid August they will not be ripe and can be left on the ground. If they are cut after August they may be ripe and the seed heads will need to be disposed off. They can be disposed of at the Garden Waste skip at Urgha recycling depot –but remember to bag the heads so as not to help the spread of the seeds.

Digging out plants: If plants are small, the easiest way to remove them is by digging them out. Small plants can often be pulled out. It is important to remove the whole of the large bulbous root from which it spreads. This can also be disposed of at the Urgha recycling depot. The leaves cannot regenerate and can be left on the ground or composted.

Herbicide Application:  Plants can be sprayed using herbicides with Glyphosate as the active ingredient. Brand-names include Roundup, Rosate, Clinic.  These herbicides are usually supplied in concentrated form and it is important to dilute according to the manufacturer’s instructions.  Whole plants can be sprayed or plants can be cut down to the base and herbicide applied to the cut stumps. The later method is safer for large plants and avoids the risk of other plants being killed or water courses being contaminated.  These herbicides are taken down into the root system, gradually weakening or killing the plant. It may take several weeks before plants show signs of dying back. Treatment over two or more years may be required to kill large plants. Hebicide can be applied June-September.

The trust plans to tackle the big problem areas, but doesn’t currently have the resources to visit individual households. We hope you will help us stop the spread of this alien species in Harris. If you need further advice, then please contact Robin Reid, North Harris Ranger, 01859 502 222


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